The following example uses getAuth() to protect a route and load the user's data. If the user is authenticated, their userId is passed to clerkClient.users.getUser(){{ target: '_blank' }} to get the current user's User{{ target: '_blank' }} object. If not authenticated, the request is rejected with a 401 status code.

// dotenv must be imported before @clerk/fastify
import 'dotenv/config'
import Fastify from 'fastify'
import { clerkClient, clerkPlugin, getAuth } from '@clerk/fastify'

const fastify = Fastify({ logger: true })

fastify.register(clerkPlugin)

// Use `getAuth()` to protect this route
fastify.get('/protected', async (request, reply) => {
  try {
    // Use `getAuth()` to access `isAuthenticated` and the user's ID
    const { isAuthenticated, userId } = getAuth(request)

    // If user isn't authenticated, return a 401 error
    if (!isAuthenticated) {
      return reply.code(401).send({ error: 'User not authenticated' })
    }

    // Use `clerkClient` to access Clerk's JS Backend SDK methods
    // and get the user's User object
    const user = await clerkClient.users.getUser(userId)

    return reply.send({
      message: 'User retrieved successfully',
      user,
    })
  } catch (error) {
    fastify.log.error(error)
    return reply.code(500).send({ error: 'Failed to retrieve user' })
  }
})

const start = async () => {
  try {
    await fastify.listen({ port: 8080 })
  } catch (error) {
    fastify.log.error(error)
    process.exit(1)
  }
}

start()